The present disclosure relates to optical thin-film based Integrated Computational Element (ICE) devices and, more particularly, to design techniques that provide favorable characteristics for ICE devices used in compact optical systems.
Compact optical systems can include optical beams having a high numerical aperture (NA). Optical beams with high NA include a number of light rays having a broad distribution of angles of incidence on the surface of optical components (normal incidence). Multilayer optical thin films in state-of-the-art optical systems are designed for normal incidence of light rays (e.g., collimated optical beams). As a result, a shift in spectral properties is expected when the multilayer optical thin film is incorporated into a compact optical system. This shift may significantly affect measurement performance of the multilayer thin film and the compact optical system as a whole. Thus, multilayer optical thin films designed for collimated incident optical beams may be rendered unusable in compact optical systems, which are otherwise desirable for use in extreme environments.
Some attempts to solve the problem of incident optical beams with high NA include vignetting the optical beam by providing spatial filters that select light rays parallel to the optical axis (i.e., forming close to normal incidence on a multilayered thin film). This approach relieves the problem of spectral accuracy of the compact optical system. However, vignetting the optical beam substantially reduces the signal-to-noise ratio (SNR) at the photo detector, in detriment of system performance.